Sclerocactus

Sclerocactus
File:Sclerocactus polyancistrus.jpg
Kingdom	Plantae
Family	Cactaceae
Subfamily	Cactoideae
Tribe	Cacteae
SubTribe
Genus	Sclerocactus
Species
Notes	Taxonomy follows Joël Lodé (2015). The genus is provisionally accepted in a narrow sense, including Toumeya.

Etymology

The name means "hard or cruel cactus", referring to the strongly hooked spines which readily attach and are difficult to remove.

Description

Sclerocactus is a genus of small to medium-sized cacti adapted to arid and often extreme environments.

• Habit: Globose to elongated cylindrical plants, solitary or forming clumps, with usually depressed apex.
• Roots: Strongly fleshy, branched or napiform root system.
• Stems: Ribbed, with distinctly tuberculate ribs.
• Spines: Dense; radial spines spreading; central spine typically hooked, often very robust.
• Flowers: Diurnal, funnel-shaped, often large; yellow, greenish-yellow, pink, magenta, purple or rarely white; self-sterile.
• Fruits: Cylindrical to elongated; dehiscent (longitudinal or lateral) or indehiscent.
• Seeds: Large, tuberculate, black, with sunken hilum; dispersal by ants (myrmecochory) and water (hydrochory).

Habitat

The genus occupies a wide range of arid habitats:

• Grasslands and desert plains
• Juniper and pine woodlands
• Limestone, gravelly and alluvial soils
• Clayey desert substrates and rocky slopes

Altitude range: from about 500 m up to 2350 m.

Some species tolerate severe frost (down to approximately −26°C).

Distribution

• United States:

Arizona, California, Colorado, Nevada, New Mexico, Texas, Utah

Taxonomy

The genus Sclerocactus was established by Britton & Rose (1922).

Its circumscription has long been controversial. Various authors have proposed broad concepts including genera such as Ancistrocactus, Echinomastus, Glandulicactus and Toumeya.

Molecular studies (Porter et al. 2000; Nyffeler 2002; Crozier 2005; Vázquez-Sánchez et al. 2013) show complex relationships within the tribe Cacteae, and indicate that some broadly defined groupings would be polyphyletic.

In a narrower concept, supported by several studies, Sclerocactus is considered monophyletic when including Toumeya.

According to Joël Lodé (2015), the genus is provisionally accepted with this circumscription.

Species

Following the classification of Joël Lodé (2015).

• Sclerocactus glaucus
  • Sclerocactus glaucus subsp. wetlandicus
• Sclerocactus mesae-verdae
• Sclerocactus nyensis
• Sclerocactus papyracanthus
• Sclerocactus parviflorus
  • Sclerocactus parviflorus subsp. havasupaiensis
  • Sclerocactus parviflorus subsp. intermedius
  • Sclerocactus parviflorus subsp. terrae-canyonae
• Sclerocactus polyancistrus
• Sclerocactus pubispinus
• Sclerocactus sileri
• Sclerocactus spinosior
  • Sclerocactus spinosior subsp. blainei
  • Sclerocactus spinosior subsp. nyensis
• Sclerocactus whipplei
  • Sclerocactus whipplei subsp. heilii
• Sclerocactus wrightiae

Notes

• The genus remains taxonomically complex and under revision.
• Some species have been previously placed in other genera such as Echinomastus or Glandulicactus.
• Sclerocactus sileri is not synonymous with Pediocactus sileri, despite historical confusion.